Manufacture of phenol



' the discovery ci llusart and Bardy rammed Dec. 3, 1929 'i UNITED v'sTATrs' PATENT.' ori-*lcs WILLIAM .T HALE AND EDGAR c. BnIrroN, or MIDLANHMICHIGAN, AssIGNons 'ro THE Dow CHEMICAL ooMI'ANY, or MIDLAND, MIcHIGAN, A CORPORATION or MICHIGAN MANUFAC'IURE or rHENon No Drawing.

In the synthetic preparation of those hydroxylic derivatives of benzene and its homologues classified as phenols, and particularlyof mono-hydric phenols,.the only process that has had any considerable commercial development is that wherein the salt ci the corresponding sulphonic acid is fused with potassium or sodium hydroxide; this despite Gompt., Rend. 7l, 105i (1872)) that chloro-benzene is hydrolyzed hy caustic soda in aqueous solution at 300 degreesxlfi. rlFhe further eirperin mental evidence touching this reaction, which was puhlished hy l. H. Meyer and ll'. Bergius (Ber. 4?', 3155 (19%)), has apparently resulted in no commercial development of the process involved.

Apparently the practical applicability of the process in question has heen rendered negative hy reason oil the corresponding relatively large amount of diphenyl ether simultaneously produced with the phenol and the alosence of any method for immediate hydrolysis or this ether without recourse to expensive caustics..

lt has been correctly notedloy Meyer ani Bergius (Vid. supra) that diphenyl oxide itsellz is markedly indifferent toward hydrol ysis hy water alone, lout that with tree allrali this hydrolysis loecornes measurable and when three molecules or alkali are present the hydrolysis approaches completion. That condif tion where chloro-'benzene was made to re-act with only one molecule ci allrali was loolred upon more particularly as a reaction lor diphenyl oxide production. presence of gto 4.@ molecules ot caustic soda, Meyer and Bergius found that chloro-hen zene, sudering lirst a simple hydrolysis to phenol and intermediate reaction of sodium phenate with free chloro-benzene to give diphenyl oxide, could not 'be made to yield over 91 per cent in phenol during rolonged (26 hours) heating at 300 degrees We have discovered, however, that the ren action between diphenyl oxide and an alkali metal phenate solution under properly controlled conditions of temperature and pressure is markedly productive of free phenol; in other words, that a salt of a strong hase Even yin, the

Application le February 21, 1923. Serial Ito. 620,486.

(e. g. sodium) and a weak acid (e. g: phenol) is found to play an exactly similarfrole to that of free caustic. lf the phenol as such is removed from. the reaction product, we have further disco'yered that the existent equilibriuro. is disturbed and that hy adding another portion of diphenyl oxide, and suhjectin the mixture to further heating, an additional quant-ity ot diphenyl voxide vwill be hydrolyzed; consequently a continuous supply of diphenyl oxide to the system maires theoretically possihle a continuous production ci phenol without addition of tree alkali.

The object of the present invention accordingly is to provide a method or `'process for making phenol wherein diphenyl oxide may he thus provided and hydrolyzed to form the desired product, To the accomplishment or this and related ends, the invention, then, consists oi the steps hereinafter Jfully described and particularly pointed out in the claims, the following description setting :torth hut one oil the various ways which the principle or the invention loe used. M

'ln practice We have proceeded substantially as follows: An aqueous solution oil sodium phenate is made up to the desired concentration and a quantity of diphenyl oxide addedthereto This mixture is then quiclrly heated in an autoclave to the temperature of the re removed, The pressure during; tte reaction i; preferably he such as to maintain sulistinin 'tial proportions at least o? the solution in. liquid phaseo Vthatever tree phenol remains in the liquor is now neutralized with 4caustic and the li uor again charged with diphenyl oxide or, w at is to the same end, with chloro benzene (which latter will re-act with a portion ol the sodium phenate present during the warming7 stage t0 give diphenyl oxide), and the mixture againA heated to reaction temperature. The sodium phenate content must ot course be held in large excess as it is the active agent in the hydrolysis ot diphenyl oxide. On stated occasions there is conducted an evaporationI of the sodium phenate liquors tor ico above.

removal of the accumulated salt followed by nal redilution before further use.

Though the possible'reaction of phenol to lose Water and to produce diphenyl oxide may be somewhat repressed by this addition of diphenyl oxide, the repression can only come about at the temperature vvhere diphenyl oxide is h drolyzed, namely, 300 degrees U. or

ven 1n the presence ot thorium oxide, as investigated and recommended to this end by Sabatier and Mailhe (Compt. Rend. 15],

492 (1910) a temperature ot/lO degrees C. was found most favorable Jfor a iitty per cent dehydration ot henol to diphenyl oxide and simultaneously tor a titty-per cent hydrolysis of diphenyl oxide to phenol. llhe comparative ease vvith which chloro-benzene re-acts upon sodium phenate to give diphenyl oxide would indicate 'there-lore that a mixture of chloro-benzene and one molecule of sodium hydroxide during initial Warming must proceed largely to the formation ot diphenyl 1 7 ',I. l. 1. oxide oetore any possioilny ot the diphenyl oxide already present to engage itself in reaction. li this vivere otherwise, We should require the addition of only a small amount of di hen l other to an ecuimolecular chloro- P y i benzene-caustic soda mixture in order to torce the chloro-benzene through its simple and complete hydrolysis to phenol and at the same time We should be able to recover the diphenyl oxide previously added. Such, however, is not the case; large quantities of diphenyl oxide may be continuously supplied to an equimolecular chloro-benzene-caustic soda solution and only very small amounts of the diphenyl oxide are ever recoverable.

ln summation', We may describe our process as one primarily constituted for the production of. free phenol by the action of diphenyl oxide upon an acqueous solution of an alkali or alkaline earth metal salt of phenol,

the process involving the removal of this free` phenol and again chargin the residual phenate solution with dipheny oxide or with any solution capable of yielding a high percentage of diphenyl oxide. Such sources of diphenyl oxide, however, should always be in more or 'less highly concentrated mixtures and pref*- erably are made up of chloro-benzene or other monohalogenated aromatic hydrocarbons and small amounts of alkali or alkalineearth metalhydroxides; the excess of chloro-benzene over the corresponding equivalent of alkali used is of course reacted upon by the sodium phenate, always present in the system in large amounts, to produce a still further quantity of diphenyl oxide. The voreging reaction may be graphically represented by the fol lowing equation, viz:

CaHlOCsHa -I- Ha0} (2051150121 ClHsONa CuHsONay When the original sodium phenate solution f is ke t constantly in very large excess ove` tem is in no Wise necessary. ln order, hovvever, to keep this large excess of sodium phenate constant, a small amount of sodium phenate should be added to the mixture after it leaves the reaction chamber or (what is the equivalent) a little free alkali should be added to this same mixture (rich in free phenol) and thus make possible the retainment of a slightly additive amount of sodium phenate in the system. lf, on the other hand, a mixture of chloro-benzene and a less than one equimolecular equivalent of caustic soda is used as a source of diphenyl oxide, there will be no need for-an additional quantity of sodium phenate tor'the reason that this diphenyl oxide producing mixture, during the initial Warming stage, does not yield its diphenyl oxide Without at the same time a certain small proportionate amount of sodium phenate. This Warmingprocess moreover must be carried on as quickly as possible so that the production of di henyl oxide is primarily favored. Such perioddoes not exproduced .Will be found combined with the i sodium hydroxide in the form of sodium phenate. This constitutes evidence of the fact that such sodium hydroxide actually enters into the reaction and distinguishes it from sodium phenate and the equivalent' compounds hereinbefore referred to which play the same role so tar as'hydrolyzing the phenyl dioxide, but do not enter into chemical combination with the resulting phenol.

In conclusion it will be observed that allV salts of strong bases and Weak acids, which 1n themselves do not bring about a substitution reaction in phenols, will function in the same manner as sodium phenate is thus seenl to function, in that they Will not enter into the reaction with the diphenyl oxide.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the method hereinI disclosed, rovided, the step or steps stated by any of t e following claims or thel equivalent of such stated step .or steps be employed. f f

l We herefore particularly point out and distinctly claim as our invention 1. A process of the character described, which comprises heating diphenyl oxide under pressure in the presence of Water and a hydrolytic catalyst salt of an alkali-forming metal, and replenishing metal.

2. A process of the character described, which comprises heating diphenyl oxide under pressure in the presence of water and a phenol salt of an alkali-forming metal.

3. A process of the character described which comprises hydrolyzing diphenyl oxide by heating under pressure in the presence of Water and sodium phenate, and replenishing the supply of diphenyl oxide.

4. A process of the character described, I

which comprises heating diphenyl oxide under pressure in the presence of water and a hydrolytic catalyst salt of an alkali-forming the supply of diphenyl oxide.

5. A process of the character described,

-Which comprises heating diphenyl oxide under pressure in the presence of water and a phenol salt of an alkali-forming metal, and replenishing the supply of diphenyl oxide.

6. A process of the character described, which comprises hydrolyzing diphenyl oxide by heating under pressure in the presence of Water and an excess of sodium phenate, re-

moving phenol and supplying additional diphenyl oxide. s

92Signed by us, this 15th day of February, 1

WILLIAM J. HALE. EDGAR C. BRITTON. 

